While there are many prior art apparatus used for the continuous heat treating process, they suffered from many short comings such as excessive working or bending of the material in the heat treating process which significantly reduces the useful life of the material heat treated.
While apparatus such as Lorig U.S. Pat. No. 2,587,742, have been utilized in the prior art, this art uses paired reels which are spaced apart to provide an annealing furnace for passing the material through the annealing furnace. The problem with the prior art of this type has been that the multiple reels require multiple bendings of the material over the multiple reels in going from a curved surface to a straight surface many times as the material is passed through the annealing oven because it must pass over two separate rollers going from straight to curved surface each time it passes over the rollers. This furnace provides working of the material which reduces its working life especially if it is a coiled tubing product. The coiled tubing product's life is to some degree a function of the number of times that the tubing is bent or worked, much like the bending of metal wire until it breaks. If in the process of the annealing, working or bending occurs in the pipe, then the overall life expectancy of the tubular pipe is greatly reduced. Thus, art such as Lorig provided a significant amount of working of the material prior to the product being exited from the annealing oven with a corresponding shortening of its useful life.
Other pieces of prior art such as U.S. Pat. No. 3,857,673, issued to Andris attempted to deal with wire and rods to be heat treated by providing a rotatable hollow drum with a plurality of passages extending therethrough. This art provided the passage for communication with the interior of the drum for attempting to provide even heat distribution to the material to be treated. One of the problems associated with Andris, however, was that heat treatment is not evenly applied to the material as large surface areas of the material were laid against the solid part of the drum and were never effectively heated in open air because it stayed against the drum all through its rotational passage until its exit from the drum. Further, the drum surfaces in contact with the material were never allowed to be reheated by re-exposure to the heated air during the materials heat treatment and thus provided uneven heat treatment of the material.
Further patents such as U.S. Pat. No. 1,243,443 issued to Pierce which have attempted to provide more heated air exposure by using loops or coils, and minimum contact of the material have proved unsuccessful. The reason Pierce was not successful was that the heat treating support structure did not provide the coils or loops with means to be controlled as they are slid sideways down the hangar or support structure. As this art was more of a batch process than a high speed heat treat furnace for continuously formed product, control of the loops or coils was not so critical in Pierce. It was, however, necessary in this prior art patent to provide for an upward curve at the free end of the hangar so as to furnish a stop against the natural sliding of the coils by gravity off the hangar. Thus, the application of the patent of Pierce would not have been appropriate for high volume, high velocity continuously formed tubing or pipe. Further, this patent really relates to heating material prior to providing it for forging of the material.
Also, many of the prior art heat treat furnaces required specialized machined surfaces to provide helical cut grooves in the cylinders for advancing the material therethrough. In such helically cut cylinders the advancing was achieved, but because of the helical surfaces needed to control the material's advancement, uneven heat treatment of the material occurred due to the excessive surface engagement of the helical surfaces and the material which prevented the lack of exposure to the heated air. Further, with machined helically cut surfaces it required a new set of surfaces with each new heat treatment time and temperature requirement which was very expensive in time and money.
There have been many prior art attempts to achieve a proper heat treating of high velocity, advancing materials located in a confined space without excessive working of the materials. These prior art attempts have been very expensive and have left the material with a reduced life and unevenly heat treated materials.